* Updates methods in nova.compute.instance_types to catchInstanceTypeNotFound exceptions and re-raise them as ApiError.
- Previously, the methods in instance_types were raising ApiError in
response to DBError, but the underlying db calls have since been
updated to detect empty results and throw more specific exceptions.
* Updates get_instance_type_by_flavor_id to not try to catch DBError,
as the underlying db call only ever raises FlavorNotFound.get_instance_type_by_flavor_id should not raise ApiError, as callers
expect the FlavorNotFound exception and know how to handle it.
* Fixes bug 872618